The present invention relates to an optical disc drive provided with an optical head including a movable lens for correcting aberration generated by an objective lens.
An optical disc, such as a CD-ROM, has a plurality of concentric tracks or a single spiral track along which data is recorded. An optical disc drive reads the data from the track of the optical disc by irradiating a laser beam thereon from an optical head and receiving the reflected light with the same optical head. The optical head is mounted on an actuator that moves radially across the optical disc so as to carry out a track-seeking operation and also to allow the laser beam to correctly trace the target track.
Recently, in accordance with the increase in the recording density and revolving speed of the optical disc, faster track seeking time and more accurate tracing of the track is required for the optical head. In order to meet such a requirement, a so-called split optics design has been developed, in which most of the optical components of the optical head is supported stationary on the optical disc drive, while an objective lens and possibly a few other optical elements are mounted on the movable actuator. The split optics design lowers the mass on the movable actuator and thus allows fast track seeking operation and also correct track tracing.
In split optics design, lenses for correcting aberration caused by the objective lens are mounted on the movable actuator since the relative distance of these lenses to the objective lens is critical for correcting the aberration.
It should be noted that the aberration caused by the objective lens is not constant but varies. One of the leading causes of the variation in the aberration is the change in the wavelength of the laser beam emitted from a semiconductor laser of the optical head in accordance with the temperature increase/decrease of the semiconductor laser. Another leading cause is the change in the shape of the objective lens due to the temperature variation thereof.
Since the aberration of the objective lens may vary as above, the aberration correcting lenses includes a lens that is moved and positioned along the optical axis of the optical head in accordance with the variation of the aberration.
The movable aberration correcting lens, however, experiences a large acceleration during the operation of the optical disc drive since the movable actuator moves quickly in the optical axis direction of the optical head during the track seeking operation and/or the track tracing process. The large acceleration forces the movable aberration correcting lens to be displaced from the desired position, resulting in low positional accuracy thereof and insufficient correction of the aberration.
Therefore, there is a need for an optical disc drive provided with an optical head that is capable of properly correcting aberration caused by an objective lens irrespective of the track seeking operation and/or track tracing operation.